---
title: "Semiconductors, Doping and the p-n Junction"
description: "A small gap lets thermal excitation put carriers into the conduction band, and impurities decide which carrier dominates. Joining two differently doped regions builds a field at the boundary that lets"
canonical: https://lightmysky.com/learn/science/semiconductors-doping-and-the-p-n-junction-mt_iKlnfAqDAg
source: https://lightmysky.com/learn/science/semiconductors-doping-and-the-p-n-junction-mt_iKlnfAqDAg.md
retrieved: 2026-09-12
---

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# Semiconductors, Doping and the p-n Junction

A small gap lets thermal excitation put carriers into the conduction band, and impurities decide which carrier dominates. Joining two differently doped regions builds a field at the boundary that lets current pass one way.

Subject: Science · Area: Matter & Materials · Ages 23 to 24
Page: https://lightmysky.com/learn/science/semiconductors-doping-and-the-p-n-junction-mt_iKlnfAqDAg

## Ready when they can

- Relates carrier concentration to gap size and temperature
- Explains what donor and acceptor doping do to the Fermi level
- Describes the built-in field of a junction and why it rectifies

## Lesson: How a junction makes current one-way

A semiconductor has a small gap, so warmth alone lifts some carriers into the conduction band. A smaller gap or a higher temperature means more carriers; that link between gap, temperature, and carrier count runs the whole story.

Impurities decide which carrier dominates. Donor doping adds electrons and lifts the Fermi level toward the conduction band, while acceptor doping leaves holes, empty seats in the nearly full band that carry current as positive charges, and pulls the Fermi level down.

**Example.** Join p-type material to n-type and carriers wander across, leaving uncovered charges behind. That charge builds a field at the boundary pointing against further crossing: the built-in field of the junction.

The built-in field is why the junction rectifies. One push direction flattens the field and current flows; the opposite direction steepens it and only a trickle passes. Current goes one way.

**Recap.** Warmth fills the band, doping picks the carrier, and the junction field opens the road in one direction only.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Band Structure: Metals, Insulators and the Gap](https://lightmysky.com/learn/science/band-structure-metals-insulators-and-the-gap-mt_9f74Vu6qnW)
- [The Grand Canonical Ensemble and the Chemical Potential](https://lightmysky.com/learn/science/the-grand-canonical-ensemble-and-the-chemical-potential-mt_sdrQrWhBAF)

## Opens up

- [Superconductivity: the Meissner Effect and Cooper Pairs](https://lightmysky.com/learn/science/superconductivity-the-meissner-effect-and-cooper-pairs-mt_2H9bAiAAUV)